The invention relates to a yarn delivery device with at least one yarn delivery roller on a textile machine comprising a drive device intended for the propulsion of the delivery roller and having a drive belt, a drive roller with a peripheral section alterable in diameter and at least in part looped around by the drive belt, and a tensioning device with a guide member acting on the drive belt and to a belt tensioning device intended for operation of the yarn delivery device.
Known yarn delivery devices of this type (DE-PS 1 286 680, de 39 31 997 A1) have a plurality of yarn delivery devices, associated with individual systems of a circular knitting machine, with delivery rollers delivering yarns, and which are rotated by a common drive belt. The drive belt is frequently propelled by a drive roller, which has a variable-diameter peripheral section at least partly looped about by the drive belt, in order to enable setting at identical rotational speed of the drive roller, different yarn delivery speeds or different delivered quantities of yarn which vary via the selection of diameter. The alteration in diameter of the drive roller can be effected manually or automatically.
Associated with the drive belt of such yarn delivery devices is an automatically operating tensioning device, which on the one hand enables enlargements in the diameter of the drive roller and on the other hand keeps the drive belt automatically tensioned during reductions in diameter, in order to avoid slippage. The tension device usually contains a tension roller, at least partly looped about by the drive belt, and which is under the influence of a force, particularly a resilient force.
A problem arising during diameter alteration of the drive roller resides in the fact that due to the tension obtaining in the drive belt comparatively large frictional forces have to be overcome, particularly when the alteration is to be effected in the direction of enlarging diameter over a large displacement path. Therefore during a manual shift of the diameter carried out when the textile machine is stopped, the tension device is frequently firstly manually so adjusted that the drive belt hangs down loosely. Such an adjustment is basically in fact possible, but is always difficult to execute if the belt tensioning device is not easily accessible, as is the case for example for circular knitting machines in which the yarn delivery device and with it the drive belt are frequently located high above the floor and are not simply accessible by the service personnel. If on the other hand alteration in the diameter of the drive roller is carried out automatically with the textile machine running, then this may only be carried out in that the alteration in diameter is undertaken only as slowly as the frictional conditions permit, which is not always acceptable.